Ethnomedicinal plants used to treat human ailments in the prehistoric place of Harla and Dengego valleys, eastern Ethiopia

Abstract

Background

Traditional medicines remained as the most affordable and easily accessible source of treatment in the primary health care system among diverse communities in Ethiopia. The Oromo community living in the prehistoric Harla and Dengego valleys has long history of ethnomedicinal know-how and practice against human and livestock ailments. However, this rich ethnomedicinal knowledge had been remained unexplored hitherto. This study focus on the comprehensive ethnomedicinal investigation in an attempt to safeguard the deteriorating ethnomedicinal knowledge that can be used as a steppingstone for phytochemical and pharmacological analysis.

Methods

Fifty five (44 male and 11 female) systematically selected informants including ten traditional herbalists (key informants) were participated in the study. Semi-structured interviews, discussions and guided field walk constituted the data collection methods. Factor of informant consensus (Fic), frequency of citation (F%), and binomial test were employed in data analysis. Medicinal plant specimens were collected, identified and kept at Herbarium of Haramaya University (HHU).

Results

A total of 83 traditional medicinal plant species against human ailments in 70 genera and 40 Families were recorded. Twelve medicinal plants were marketable in open market places of the nearby towns. Formulations recorded added to 140 remedies for 81 human ailments. Concoction accounts 50.7% of the total preparations followed by fluids extraction (10.7%) and infusion (6.4%). Fifteen different plant parts were used for remedies preparation wherein leaves accounted 46.4%, stem 9.2%, fruits and roots each 7.8%. Most of the remedies (90.7%) were prepared from single plant species like, aphrodisiac fresh rhizome of Kleinia abyssinica (A. Rich.) A. Berger chewed and swallowed few hours before sexual performance for a man having problem of erectile dysfunction. The Fic value ranges between 1.0 (gastritis and heartburn/pyrosis) and 0.77 (swollen body part). Aloe harlana Reynolds was reported to be used for the highest number of ailments treating swollen body part locally called GOFLA, colon cleaner, snake bite, liver swelling, spleen swelling/splenomegaly, fungal infections and inflammation of skin.

Conclusion

Such documentation of comprehensive ethnomedicinal knowledge is very valuable and needs to be scaled-up so that it could be followed up with phytochemical and pharmacological analyses in order to give scientific ground to the ethnomedicinal knowledge.

Background

Knowledge of the medicinal plants of Ethiopia and their uses provide wide and vital contribution to human and livestock healthcare needs throughout the country [1–5]. These wide and vital uses of traditional medicine in the country could be attributed to cultural diversity and acceptability, psychological comfort, economic affordability, and perceived efficacy against certain type of diseases as compared to modern medicines [6, 7]. In Ethiopia, about 80% of the human population and 90% of livestock is said to be dependent on traditional medicine for primary healthcare services and most of this comes from plants [8, 9]. That is why there are considerable number of research works on the various aspects on traditional medicinal plants [2, 5–7, 9–17] even some were developed to the pharmaceutical industries like, Phytolacca dodecandra L’Herit. [18, 19]. However, many more medicinal plants of Ethiopia which are found in lesser studied areas still anticipate scientific studies.

The reviewed literatures show that studies on medicinal plants of Ethiopia have so far concentrated in the south, southwest, central, north and north-western parts of the country [2, 5–7, 9–13, 15, 16, 20–33]. There were little data that quantitatively assess the resource potential, indigenous knowledge on the use and management of medicinal plant species from eastern Ethiopia [34, 35] as well as none are there from the present study area.

The Oromo people who currently inhabit the prehistoric Harla and the entire catchments might be the descendents of the former Harla people of the Harla kingdom which had been ruled between 13^th to 16^th centuries (Patacini D, Berehanu K: Notes on Harla: a preliminary report, Unpublished). They are expected to be the guardians of valuable indigenous knowledge on the use of traditional medicinal plants of their surroundings, which they use for treating human and livestock ailments. Scientific investigations indicated that there is an endemic plant species named after this prehistoric place called Aloe harlana Reynolds [36] due to its availability only in Harla locality. It has been traditionally used by the Oromo people in Harla for the treatment of various infectious and inflammatory diseases [17]. The latex and isolated compounds of A. harlana possess promising antimicrobial activity particularly against the Gram-negative bacterial strains such as Escherichia coli, Salmonella typhi and Vibrio cholerae[17]. Unpublished documents suggested that there are many more potential medicinal plants in this unique geographic setting and complex landscape areas.

Even one of the translations of the eastern port town of Ethiopia known as Dire Dawa is “plain of medicine” in Oromo language. Dire Dawa is only 15 kms far from Harla and this study also covers 5 to 25 kms distant areas from this village believing that most of the traditional medicinal plants which are marketable in Dire Dawa are coming from these study areas (Harla and Dengego valleys and the entire catchments of Dire Dawa). In addition, given the diversity of plant species in the Dengego Mountains and valley complex, and the ancient history and civilization of the vanished Harla Kingdom, the share of medicinal plants and the value of the associated indigenous knowledge of the current Oromo communities of the area, who might be descendents of the lost Harla people, is expected to be high.

However, except few archaeological studies [23, 37], this prehistoric place and people, Dire Dawa and entire Dengego mountain and valley complex are ethnobotanically unexplored and there is no comprehensive account of the traditional medicinal practices. Therefore, the objectives of this study were to (1) assess, identify and document the traditional medicinal plant species potential; (2) investigate comprehensive information on associated indigenous knowledge of medicinal plants; (3) generate baseline ethnomedicinal information on medicinal plants for human ailments for further investigation. Thus, the output of this study can be used as a steppingstone for conservation of medicinal plant species, preservation of ethnomedicinal knowledge, and phytochemical and pharmacological analysis.

Methods

Study area

The study area covers Harla upto Biyo Awale and Dengego Mountains and Valleys complex which is found under Dire Dawa administrative council. It extends 5 to 25 kms distance SE of Dire Dawa town in eastern Ethiopia which is located at 515 kms east of Addis Ababa and 311kms west of Djibouti.

This area is delimited with coordinates of 9°27′ and 9°39′N latitude and 41°38′ and 42°20′E longitude. Its elevation ranges between 950–2260 meters a.s.l. (Figure 1). The physiographic feature includes mountain ranges, hills, valleys, river terraces and flat plains. The geology of the area consists of precambrian metamorphic rocks (Gneisses, pegmatites and diorites), mesozoic sedimentary rocks (Adigrat sandstone, Hamanlei limestone and Amba Aradam sandstone), Tertiary volcanic (basalts) and quaternary sediments (alluvial sediments, travertine and river sand deposits) [38].

Figure 1

Map of study area indicating the prehistoric Harla with neighbouring kebeles and Dengego mountains/valleys complex.

The mean annual temperature is about 22.8°C, ranging from a mean minimum of 16.2°C to mean maximum of 30.4°C. May to June are the hottest months of the area; whereas, November to January are the coldest months. The mean annual rainfall in the surrounding areas ranges from about 1,000 mm on the south to about 500 to 600 mm in the north lowland. Almost all of the catchments receive less than 900 mm year^-1 of rainfall. Rainfall is bimodal, occurring from February to April (short rainy season) and June to September (long rainy season). The mean annual runoff values estimated for different watersheds ranges from 12.4 Mm³ to 100.13 Mm³[39].

The human population of the rural area is about 125, 800 (Male 63,000 and 62,800 female) in which the livelihood depends mainly on smallholder agriculture and livestock production [38]. The vegetation of the area includes few grass lands and wood lands, scrubland and bush lands dominated by species like Acacia brevispica Harms, A. bussei Harms ex Sjostedt, A. etbaica Schweinf, A. seyal Del., Aloe megalacantha Baker, A. harlana Reynolds, Balanites aegyptiaca (L.) Del. Euclea racemosa Murr., Euphorbia bergeri M. Gilbert, Ficus salicifolia Vahl. Opuntia ficus-indica (L.) Miller, and O. stricta Haworth.

Harla is probably a 13^th C village. As the finding of the site indicated, it has a long time commercial link with the middle and Far East through the port of Zeila between 13^th and 16^th C (Patacini D, Berehanu K: Notes on Harla: a preliminary report, Unpublished). The whole village was buried beneath the surface and covered with ashes and pumice. The current Harla is built on top of the old one. The current inhabitants use ready rectangular stone blocks from the old village, which they have uncovered while digging below the surface, to build their homes, fences, and farm land terraces (Pers. Observation and communication).

There are very limited written documents on the history of the Harla kingdom. Due to limitation of published works on the prehistoric Harla, we are unable to mention many references in this study except for a few indicated issues that may attract field professionals for future investigations. Of course, there are certain archaeological findings collected by different social anthropologists and archaeologists that are kept for visitors in the small museum at the centre of Harla village. Archaeological findings and collections of the site include coins written in Arabic and Chinese, pieces of glasses, ornaments, tools for knitting, pottery fragments and a stone moon calendar with two geographical coordinates, etc. which are available in some homes of the residents and in the small museum at the centre of Harla village (Pers. observation).

Data collection methods

Participatory Rural Appraisal (PRA) techniques were employed to collect data, as recommended by Martin [40] and Cunningham [41]. Employing this methodology, an ethnobotanical data were collected in two different rounds, from October to December 2012 and May 2013 from six sampling sites which were identified from the study areas namely Biyo Harla, Gende Biyo, Mudi Adi, Tabiya, Menchitu and Biyo Awale. The first three sites were villages in Harla kebele and the other three sites were purposively selected as neighbouring kebeles (the smallest political administrative unit in Ethiopia) of the prehistoric Harla to represent Dengego valley complex. Ethnobotanical information was collected from 55 informants (44 male and 11 female). Among the 55 informants, 10 key informants (traditional healers) were selected with the assistance of community leaders, elderly people and members of the local community. Purposive sampling technique was used for selecting key informants (all were male and above 55 age) while stratified random sampling was employed to select others (34 male and 11 female). Households of selected study sites were registered and stratified into three age groups. Then fifteen informants were randomly selected from each stratum (age group) to see how the knowledge varies with age. The three age groups were young (25–40), adult (41–60) and elderly (above 60).

Before carrying out the interviews and group discussions, a traditional ceremonial and blessing of the Oromo culture conducted and an oral Prior Informed Consent (PIC) was confirmed from every respondent. Furthermore, participants collectively endorsed the research by giving oral blessings in their usual traditional style. Semi-structured interviews with 55 informants and group discussions (total of 9 groups discussed with average members of 11 per group) were administered in the local language (Afan Oromo) to collect basic information on the local name(s) and traditional description of the medicinal plant species, diseases treated or controlled, parts used, conditions and method of preparations, routes of remedial administration, dosages used, major drawbacks, and locally marketable medicinal plants. Besides, practical observation sessions in preparation of remedies and some observation of traditional treatment given to the patients by traditional healers were conducted. In addition, guided field walks with key informants were employed to collect voucher specimens of each medicinal plant species with additional notes. Photographic cameras were used for graphic documentation. Additional interviews with key informants were carried out in the field in order to avoid the risk of confusing identity of plant species by repeated inquiries. This was done for at least three times with the same and different informants so as to confirm the validity and reliability of the recorded information. Specimens were collected and numbered on the spot, later identified using taxonomic keys in the relevant volumes of the Flora of Ethiopia and Eritrea and through visual comparisons with authenticated plant specimens kept at the Herbarium of Haramaya University (HHU) where voucher specimens of the medicinal plants were deposited. The authentication of identified plant species was done by a renowned plant taxonomist, Mr. Melaku Wondafrash (National Herbarium of Addis Ababa University).

Data analysis

The data were filled in Excel sheet in a way that makes the analysis very suitable. Total number of traditional medicinal plant species used for human ailments along with their Family and genus distribution; growth habit in percentage; part used versus number of remedies prepared; number of human ailments treated; methods of preparation, and route of administration were all analyzed using both qualitative and quantitative methods following Martin [40] and Cotton [42]. The informant consensus factor (Fic) of each medicinal plant, the proportion of informants who independently reported its use against a particular disease/disease category, was calculated using the formula: Fic = n _ur –n _t /n _ur –1 [43, 44], where, n _ur is the “number of use-reports” in each disease category and n _t is the “number of taxa used”. The Fic values range from 0 to 1, with high values (i.e. close and equal to 1) indicating that relatively few plants are used by a large proportion of informants, while low values (<0.5) indicate that informants do not agree on the plant species to be used to treat a category of ailments.

Frequency of citation (F) of each medicinal plant species was calculated using the formula:

$$\begin{array}{ll}F\left(\%\right)=& \mathit{No}.\mathit{of}\mathit{informants}\mathit{who}\mathit{cites}\mathit{the}\mathit{species}/\\ \mathit{Total}\mathit{No}.\mathit{of}\mathit{informants}\times 100.\end{array}$$

Binomial test was run in SPSS 18.0 to evaluate the depth of knowledge with age categories in which pair wise age category test was considered and for comparison of gender wise depth of knowledge. P-value of less than 0.05 was taken as statistically significant difference. MS Excel Spreadsheet was used to generate bar graphs.

Results and discussion

Medicinal plant species richness and part used for remedial preparations

This study revealed that the prehistoric Harla and Dengego Mountains and Valleys complex harbour about 83 traditional medicinal plant species against 81 human ailments which are distributed across 70 genera and 40 Families (Table 1). About 57.8% of these traditional medicinal plant species belong to ten Families. Asteraceae had the largest number of plant species (10, 12%), followed by Fabaceae (8, 9.6%), Euphorbiaceae (6, 7.2%) and Cucurbitaceae (5, 6%). Aloaceae and Lamiaceae had each 4 plant species, Asclepiadaceae, Boraginaceae and Capparidaceae each has 3 species, and Apocynaceae has 2 species. About 71% of these medicinal plant species were reported by different authors who conducted researches on traditional medicinal plants in the different parts of Ethiopia [4–7, 9–13, 15, 16, 21, 22, 24, 25],[27–32, 34, 45] wherein about 44% of them were reported for similar ailments. The number of medicinal plant species reported in this study is considerable, though application of long-term participant observation techniques could add more medicinal plant species to the present list, given the floristic richness and the strongly plant-based bio-cultural background of the people. In addition, there is a potential market of traditional medicine in the nearby towns like Dire Dawa stretching to Djibouti. That is why few traditional practitioners were reluctant to give all the information since this could be detrimental to the economic benefits that come out of the traditional medicine. So, the economic benefits coming out of the traditional medicine restricted the information to some extent.

Table 1 List of traditional medicinal plant species used to treat human ailments in the prehistoric Harla and Dengego valleys

Among the medicinal plants identified in this study, various parts of 12 medicinal plants species were reported to be sold in the open markets of the nearby towns like Dire Dawa. The dried and powdered sap of Aloe harlana and A. megalacantha, seeds and leaves of Azadirachta indica, leaves of Gloriosa superba and Lawsonia inermis; and the fresh root of Cissampelos mucronata, tuber of Coccinia sp., leaf of Ocimum lamiifolium, fruits of Punica granatum and Tamarindus indica were sold in the open local market places. Similarly, ample domestic trade of Ethiopian medicinal plants was reported for diverse cultural groups in Ethiopia [6, 7, 16, 21, 23, 26, 34]. In contrary, none of the medicinal plants reported by some other studies were available for sale in local markets [2, 5, 10]. These might be related with the norm and cultural issues of diverse communities who permit and prohibit marketing of traditional medicines.

Analysis of the growth habits of the traditional medicinal plant species showed that shrubs constitute the highest number of species and epiphytes the least number of species, represented by only one species (Erianthemum aethiopicum/Loranthaceae) (Table 2).

Table 2 The number of traditional medicinal plant species in each growth habit

The highest proportion of growth habit was covered by shrubs and herbs that constitute 68% of the total traditional medicinal plants. This can be related to the floristic composition of vegetation, which is dominated by woodland, bushland and scrubland vegetation types both in valleys and rocky mountains. Similar patterns were reported by some medicinal plant inventories work [16, 24, 25] where shrubs and herbs are the largest plant growth habits but contrary to some works [6, 34] where woody plant species dominated the growth form.

A total of 15 different parts of the medicinal plant species are used for remedies preparation (Figure 2). Remedial preparations made from leaves accounted for 46.4%, stem 9.2%, fruits and roots each 7.8% of the total preparations. This could be a large number of plant parts used in remedial preparation when compared with the various research reports done on traditional medicinal plants [15, 21, 22, 28–30, 34]. Such diversified use of plant parts in remedial preparation could be considered as an indicator of the deep rooted and long lasting practice and know-how of traditional medicinal plants by the community.

Figure 2

The use of different plant parts in remedial preparation and number of preparations per plant part.

A total of 140 preparations were made using these 15 different parts of the medicinal plant species. The most frequently sought parts of the medicinal plant species were leaf, fruit, seed, branches, pod, and nectar that account for 60%. This may lead to the conclusion that harvesting medicinal plants poses no significant threat to the natural vegetation of the study area. Similarly, in studies conducted elsewhere in Ethiopia, leaf was indicated to be the most frequently used plant part in remedial preparations that do not cause any significant threat to the survival of individual plants when compared to other plant parts such as underground part, stem, bark and whole plant [2, 15, 16, 34, 46]. In contrast, other studies [30–32] indicated root and bark as the most commonly harvested plant part for remedial preparations. For example, study conducted in Benshangul-Gumuz of Ethiopia [30] reported that about 63% of the preparations were made from root and bark of medicinal plants. It is a mere fact that medicinal plants that are harvested for their roots, rhizomes, bulbs, bark, stem and whole part have severe effects on their survival [1, 3] but this could be more important for the perennial and woody plant species.

Informant consensus factor and frequency of citation

The most common health problems of the population of the study area were identified by traditional healers based on their experience on frequency of ailments treatment. In this respect, a total of 11 ailments were reported as the most common health problem of the study area. The Fic value for these most important health problems of the area ranges between 0.77 and 1 (Table 3). The Fic is higher for gastritis and heartburn/pyrosis (1.0) and relatively lower for swollen body part locally called gofla (0.77). The Fic results could be useful in prioritizing medicinal plant species for further pharmacological studies [10, 25] since efficacy of traditional medicinal plant is strongly correlated with Fic value, meaning pharmacologically effective remedies are expected to have greater Fic value and vise versa [43].

Table 3 Major types of human health problems of the study area, number of plant species used and informant consensus factor values

Even if the highest value of Fic was for gastritis and heartburn/pyrosis indicating that there is high consensus on the treatment of these major health problems of the area, it can be concluded that there are relatively high Fic values for their major health problems. This will attract pharmacologists for further pharmacological investigation of the traditional plant species in this rich ethnomedicinal knowledge and practice centre. The pharmacological study done in the prehistoric place of Harla by [17] indicated that the latex and isolated compounds of A. harlana possess promising antimicrobial activity particularly against the Gram-negative bacterial strains such as Escherichia coli, Salmonella typhi and Vibrio cholerae. Similar results were reported by [6, 47] where the Fic value were greater than 0.5 for all clusters that may encourage interested researchers for validation of bioactivity as well as isolation and characterization of the active principles of those plant species in each category with high frequency of citation.

The frequencies of citation for medicinal plant species that are more popular and widely used by the local community were analyzed. Species having more than 20% frequency of citation are given in Table 4. A total of 18 plant species showed high frequency of citations ranging from 21.8–87.3 percent. Aloe megalacantha has the highest frequency of citation (87.3%) which was used as colon cleaner and a remedy made from it locally called sibri is sold in the local open market places, followed by Cissampelos mucronata (85.5%), Aloe harlana (78.2%), Ocimum lamiifolium (76.4), etc. (Table 4). This can show substantial level of agreement on the therapeutic worth of the traditional medicinal plant species in the study area. The greatest independent citations a particular species receives for treatment of a certain illness category is, the greatest its cultural importance [34].

Table 4 Plant species with the highest frequency of citation based on overall effectiveness to treat the corresponding human ailments

Aloe harlana was reported to be used for the highest number of ailments that treat swollen body part locally called gofla, anti-poison for snake bite, liver swelling, spleen swelling, colon cleaner, skin and hair fungus and skin inflammation. Another study [17] on A. harlana indicated that the Oromo people in Harla have been used it for the treatment of various infectious and inflammatory diseases. It has a considerable role in the primary healthcare system of the community. It is an endemic plant species known only in this study area and the specific epithet “harlana” refers to the prehistoric Harla, locality of type specimen. Until the time of this study, the community in Harla didn’t know that the famous and endemic traditional medicinal plant known as A. harlana is only found in their vicinity and nowhere else. Its sap extraction was dried, crystallized and powdered for the preparation of a popular traditional colon cleaner locally known as sibri (Oromo language), a product name on local market places. Indeed, this result will encourage local communities to further conserve and safeguard such valuable medicinal plant species within their ongoing wide scale conservation activities. A study conducted in Arsi zone of Ethiopia [29, 33] indicated that paying special attention to high value medicinal plants could help to strengthen the role of those plant species in healthcare and environmental protection.

Plant species such as Aloe megalacantha, Cissampelos mucronata, Ocimum lamiifolium, Tamarindus indica, Lawsonia inermis and Withania somnifera scored high frequency of citations greater than 50 percent among the medicinal plant species which were marketable in the open market places. The higher frequency of citation of these species indicates their importance for local communities and attracts more attention for conservation in the study area.

The result on depth of comprehensive ethnomedicinal knowledge among different age groups indicated that elderly people (above 60 years) had much profound knowledge (binomial test, p = 0.002). Whereas, an ethnomedicinal knowledge test in the age group ranging from 25 to 40 showed the least value (binomial test, p = 0.008). There is a significant difference in the depth of ethnomedicinal knowledge between age category ranging from 25 to 40 and age category above 60 (p > 0.05). It was observed that many young people in the study area are less knowledgeable about the variety and value of indigenous medicinal plants. This might be attributed to the current expansion of education and health centres to kebele level which has resulted in the young generation focusing on modern medicines. Similar results were reported in some other cultural groups in Ethiopia [15, 26] that showed the deterioration of indigenous knowledge on medicinal plants throughout the generations. A study conducted in Bale region of Ethiopia witnessed that western style health care services provided by government and NGOs seem to have contributed to a decline in traditional knowledge on medicine [28]. Therefore, documentation and communication of findings on knowledge and use of traditional medicinal plants in the present study area and beyond is very valuable in safeguarding the deterioration of indigenous knowledge on medicinal plants. Such findings need to be scaled-up followed by phytochemical and pharmacological analyses in order to give scientific ground to the ethnomedicinal knowledge.

In addition, the binomial test on ethnomedicinal knowledge between men and women showed that men have much more profound knowledge (binomial test, p = 0.001) than women (binomial test, p = 0.009) which is significantly different (p > 0.05). Similar results were reported by [9–11, 34] where men have more profound knowledge than women in many parts of Ethiopia. This might be related with the local tradition of restricting traditional medical practices mostly to men and resulted in least number of women representation in the informant sampling of this stud. All the key informants (traditional healers) selected in this study were men, as it is also largely true for many other parts of Ethiopia. In contrast, [48] have reported women have more specialized knowledge on medicinal plants than men since they are often called upon to diagnose and treat certain types of diseases. It was also reported that men and women who are traditional medicine practitioners have relatively equivalent medicinal plants knowledge [26].

Methods of preparation and routes of administration

The informants reported that 140 different preparations were made from 83 medicinal plant species. These were cited in the traditional healing system for use in 81 different human ailments. Out of the total preparations 50.7% are prepared in the form of concoction followed by fluids extraction (10.7%) and infusion (6.4%) (Table 5). Most of the remedies are prepared from a single species; mixtures are used infrequently. Out of total preparations, 127 were prepared from single plant species and the rest 13 were from two or more plant species. A number of sources [2, 10, 11, 27, 45, 49] reported similar results stating that monotherapy preparation made from single plant species was used more frequently than mixtures for remedy preparations. This contrasts with the report by [9, 15] where mixtures of different species were used to treat ailments than the use of single species.

Table 5 Method of preparation

The preparations made from mixture of two plant species were like, the bark of Croton macrostachyus and Terminalia brownii were crushed, concocted and taken orally to treat jaundice. The stem and leaf of Kalanchoe marmorata and the seeds of Ricinus communis were crushed together and bandaged to treat small skin swelling with pus resulting due to poisonous spines. The bark and leaf of Cadaba rotundifolia and Withania somnifera were concocted together to treat extended flow of menstruation. Fruit and leaf of Cucumis dipsaceus and Commicarpus sinuatus were concocted together and taken orally to treat gonorrhoea. An oily extract from the leaf of Kleinia longiflora was boiled and mixed with crushed fresh leaf of Cadaba rotundifolia. It is used to massage paralyzed body part every morning and evening to improve nerve function. It was also reported that the fresh leaf of Gloriosa superba was crushed with succulent stem of Caralluma speciosa and applied on the starting point of gangrene so as to prevent its’ spreading to the rest of the body.

The fresh leaves of three plants i.e. Steganotaenia araliacea, Grewia bicolor, and Cissampelos mucronata were concocted together and taken orally for a person having mental disturbance and body burning feeling. This was the only remedy made from mixture of three plant species. According to traditional healers’ report this remedy has body cooling effect, giving good sleep and mental stability when a small cup of solution is taken in the evening. Some of the traditional healers mentioned that the use of multiple therapies in traditional remedial preparation could increase the efficacy of traditional medicine for the corresponding health problem. According to [50], the use of more than one plant species to prepare a remedy for ailments is attributed to additives or synergistic effects during ailment treatment.

In addition, different plant parts from a single species were prepared in similar ways to treat different types of aliments. For example, the infusion from fresh leaf and seed of Azadirachta indica is taken orally to treat malaria and intestinal parasites; the leaf and root of Craterostigma plantagineum were concocted together and taken orally to treat liver disease and diarrhoea; leaf and jel of Aloe harlana were concocted together and used as an ointment to treat skin and hair fungi. Some remedial preparations need admixture like oil, honey and sugar. These could increase the adhesive nature of remedies particularly for dermal ailments. They also reduce some side effects like bitterness, vomiting; and improve the taste of remedies. Other studies [5, 11, 23, 25, 27] also reported about the use of admixtures in remedial preparations for same effects.

Both internal (55.1%) and external (44.9%) routes were used for application of the medicines. For internal application, the most common route was oral that accounted for 45.7% and that of external was dermal ointment which accounted for 12.1% (Table 6). Though, more diversified usage was reported for external use (nine different ways), oral route of administration accounts the highest percentage. Some more studies reported that oral route of administration is the most common [15, 25–27, 34].

Table 6 Routes of administration

There was no consensus on the dosage used and frequency of medication among the traditional healers. Most of them reported that the dose given to patients depended on age, physical and health conditions. For example, a small piece of an aphrodisiac fresh rhizome of Kleinia abyssinica can be enough if properly chewed and swallowed few hours before sexual performance to increase sexual performance of physically weak and less weighted person/man whereas considerably large sized rhizome is needed for same effect for stronger and heavy weighted person/man having problem of sexual dysfunction. Lack of precision and standardization was mentioned as a global drawback of traditional healthcare system [4, 27, 45]. Similarly, in this study where internal route of application accounts 55.1%, lack of precision can be taken as the major drawback.

Overdose of remedies was also reported to bring adverse effects like, diarrhoea, vomiting, abdominal pain, unconsciousness, and fainting of the patient. During such incident, the traditional healers use different antidotes for reversing adverse effects like, “hoja” a local hot beverage prepared from milk and pericarp of coffee berry, coffee, honey and milk. The same pattern of using antidotes was reported for other cultural groups elsewhere in Ethiopia [5, 9, 11, 26, 45].

Conclusion

Overall, this comprehensive ethnomedicinal study showed that the community in Harla and Dengego Valleys rely on considerable number of traditional medicinal plant species to treat wide spectrum of human ailments and are knowledgeable about the identities and applications of medicinal plants. The majority of medicinal plant species were harvested for their leaves so poses no significant threat to the natural vegetation of the study area. Out of the total ethnomedicinal plant species identified in this study some were endemic plant species like, Aloe harlana, Aloe mcloughlinii, Gomphocarpus purpurascens, Indigofera ellenbeckii and Rhynchosia erlangeri. Among these endemic medicinal plant species, Aloe harlana was found only in this study area. It had been named after the prehistoric Harla. It was the first time for the local community to get this information. They were highly excited and encouraged to further conserve and safeguard such valuable medicinal plant species within their wide scale conservation activities.

Plant species like, Aloe megalacantha, Cissampelos mucronata, Ocimum lamiifolium, Tamarindus indica, Lawsonia inermis and Withania somnifera scored a high frequency of citations (>50%) among the medicinal plant species which were marketable in the open market places. Such benefits of plants in the primary healthcare system, income generation and higher frequency of citation could be considered as a good opportunity for the support of their livelihood. Therefore, the out put of this comprehensive ethnomedicinal knowledge will encourage the community to conserve, manage and sustainable use the medicinal plant species.

The binomial test on the depth of ethnomedicinal knowledge between younger and elderly informants showed a significant difference. Many young people were less knowledgeable about the variety and value of traditional medicinal plants. This showed the level of deterioration of ethnomedicinal knowledge in this prehistoric study area. It is, therefore, necessary to preserve this indigenous knowledge on traditional medicines by proper documentation, identification of plant species, herbal preparation and dosage. In addition, it should be followed with phytochemical and pharmacological analyses in order to give scientific ground to the ethnomedicinal knowledge.